Earth in Space Section 19.1

Earth’s Shape Considered to be ellipsoid Oblate spheroid Earth is wider than it is tall Bulges at equator, flattened at poles

Earth’s motions Rotation – spinning on an axis - causes day and night

Earth’s Motions 1. sidereal day The time it takes the Earth to rotate once with respect to a reference star. One 360° Rotation Time = 23 hr. 56 min. 1-2: Globe rotates 360° - sidereal 1-3: Globe re-points to sun - synodic

Earth’s motions 2. solar (synodic) day = 24 hours The time it takes Earth to rotate once with respect to the sun. (Sun’s Highest point in sky to the next highest point in sky).

Earth’s Motions Revolution – movement around a fixed point (sun)

Earth’s Motions - Revolves once every 365.25 days (year) need leap years - elliptical shaped orbit - Jan. 3 - 147 million km from sun (perihelion) - July 4 - 152 million km from sun (aphelion)

Seasons on Earth Earth’s axis is tilted 23.5o The area tilted towards sun has longer days and more radiant energy (summer) The area tilted away from the sun has shorter days and less radiant energy (winter)

Vernal equinox March 20 or 21 Solstice – the sun reaches the greatest distance north or south of the equator Summer solstice June 21 or 22 Longest day Winter solstice Dec 21 or 22 Shortest day Equinox- the sun is directly above the equator. Equal daylight and night time hours all over the world Autumnal equinox Sept 22 or 23

Earth’s Motions Precession – Earth’s wobble

Earth’s Orbit Law of universal gravitation: every object in the universe attracts every other object. Isaac Newton

Attracts all objects towards each other.

Depends on two factors: MASS DISTANCE The amount of matter (stuff) in an object STRONGER

MASS WEIGHT The amount of matter (stuff) in an object Does not change VS The amount of matter (stuff) in an object Does not change Force ( a push or pull) of gravity on an object. Changes depending on where you are.

265 lbs =120 x 1.6 About 45 lbs

Earth’s Orbit Inertia – the tendency of an object to resist change in motion Newton’s first law of motion An object in motion will stay in motion, in straight line, at a constant speed unless acted upon by an outside force

Earth’s Orbit Newton concluded that 2 forces (inertia, gravity) Inertial force Newton concluded that 2 forces (inertia, gravity) combine to keep Earth in orbit around the sun Gravitational force Earth’s motion around the sun, Not as easy as I thought